Barrier coatings and barrier layers are used in a variety of applications; for example absorbent materials, nonwovens, textiles and paper. They are particularly important in absorbent materials where the barrier coating or barrier layer prevents any of the absorbed liquid from penetrating the side opposite of the absorbent surface. This is important for such products as absorbent pads, disposable childrens bibs, and medical hygiene products. Barrier coatings are also important for monolithic substrates where the coated substrate is used to prevent aqueous liquid penetration, thus protecting adjacent surfaces.
Absorbent materials are typically multi-layered in construction and can comprise a liquid-permeable cover sheet having one side designed for placement in contact with the wearer or food, an absorbent section, and an impervious backsheet. Polyolefin film such as polyethylene or polyproplyene-films are typically used as a backsheet for absorbent pads because it prevents passage of aqueous fluids to the opposite side of the film. In some cases, the polyolefin film is perforated in such a way as to allow water vapor to pass through the film but inhibits the passage of aqueous fluids. However, there are drawbacks to the use of polyethylene film for absorbent pads. For example, it is sometimes difficult to place and attach the polyethylene film to a substrate, creating waste when it skews off the substrate during secondary operations. In some cases, application of an adhesive, such as a hot melt adhesive, or some other method of attachment is needed to keep the polyethylene film in place. Also, the polyethylene film needs to be applied in a secondary operation that is separate from the production of the absorbent pad, textile or nonwoven. A more practical substitute for the polyethylene backsheet would therefore benefit the industry.
Examples of coatings used as water repellents are:
Colbert (“Fluorochemicals—fluid repellency for nonwoven substrates” (TAPPI, September 1976, Vol. 59, No.9, pages 129-131)) discloses the use of fluorochemicals to provide fluid repellency to nonwoven substrates without the formation of continuous film barriers.
U.S. Pat. No. 4,062,818 (Mate, 1977) discloses an aqueous composition which imparts both flame resistance and water repellency properties to nonwoven textiles. The composition contains a poly(vinyl acetate), a chloro- or bromo-substituted phosphate plasticizer, a polyfluoroalkyl polyacrylate, water repellent, and an inorganic, water soluble salt.
U.S. Pat. No. 3,912,674 (Stahl, 1975) discloses a water repellent coating made up of an ethylene ionic copolymer, a paraffin wax, and a terpolymer of vinyl acetate, ethylene, and N-methylol acrylamide. The ethylene copolymer dispersion is held in dispersed phase by means of an amine soap surfactant.
WO98/14078 (Baumann, et al., 1998) discloses a face mask that allows gas to pass through while inhibiting passage of liquid through it. The mask includes a face-contacting layer, an outer cover layer, a polymeric microfiber mat disposed between the face-contacting layer and the outer cover sheet, and a non-woven fibrous mat disposed between the face-contacting layer and the outer cover sheet. The non-woven fibrous mat includes polymeric fibers and a surface energy reducing agent, such as a fluorochemical, a wax, a silicon or a combination thereof.
US 2001/0021616 A1 and U.S. Pat. No. 6,251,210 B1 (Bullock et al, 2001) disclose a method of preparing a stain resistant and water repellant textile fabric in which the fabric is first treated with a fluorochemical textile treatment composition and dried at elevated temperature. The treated fabric is then provided with a polymeric film to one side of the treated fabric and dried again at elevated temperature. A detackifying wax may be part of the secondary treatment composition.